1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to ferromagnetically coupled magnetic recording media.
2. Description of the Related Art
Conventional disc drives are used to magnetically record, store and retrieve digital data. Data is recorded to and retrieved from one or more discs that are rotated at more than one thousand revolutions per minute (rpm) by a motor. The data is recorded and retrieved from the discs by an array of vertically aligned read/write head assemblies, which are controllably moved from data track to data track by an actuator assembly.
The three major components making up a conventional hard disc drive are magnetic media, read/write head assemblies and motors. Magnetic media, which is used as a medium to magnetically store digital data, typically includes a layered structure, of which at least one of the layers is made of a magnetic material, such as CoCrPtB, having high coercivity and high remnant moment. The read/write head assemblies typically include a read sensor and a writing coil carried on an air bearing slider attached to an actuator. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. The actuator is used to move the heads from track to track and is of the type usually referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing closely adjacent to the outer diameter of the discs. Motors, which are used to spin the magnetic media at rates of higher than 1,000 revolutions per minute (rpm), typically include brushless direct current (DC) motors. The structure of disc drives is well known.
Magnetic media can be locally magnetized by a read/write head, which creates a highly concentrated magnetic field that alternates direction based upon bits of the information being stored. The highly concentrated localized magnetic field produced by the read/write head magnetizes the grains of the magnetic media at that location, provided the magnetic field is greater than the coercivity of the magnetic media. The grains retain a remnant magnetization after the magnetic field is removed, which points in the same direction of the magnetic field. A read/write head that produces an electrical response to a magnetic signal can then read the magnetization of the magnetic media.
Magnetic media structures are typically made to include a series of thin films deposited on top of aluminum substrates, ceramic substrates or glass substrates. FIG. 1 illustrates a conventional anti-ferromagnetically coupled magnetic media structure having a substrate 110, a seed layer 115, a first ferromagnetic layer 120, an anti-ferromagnetic coupling layer 125, a second ferromagnetic layer 130, and a protective overcoat 140.
Substrate 110 is typically made of Aluminum (Al), nickel-phosphorus plated aluminum, glass or ceramic. Seed layer 115 is typically made of Cr or a Cr alloy and can be less than 200 angstroms. First ferromagnetic layer 120 is the stabilization layer and can be made of a ferromagnetic material such as Co. Second ferromagnetic layer 130 is the main recording layer and is also made of a ferromagnetic material such as Co. Anti-ferromagnetic coupling (AFC) layer 125 is made of Ru and is used to anti-ferromagnetically couple the main recording layer with the stabilization layer.
In AFC media the main recording layer is anti-ferromagnetically coupled across a Ru spacer layer with the thin magnetic stabilization layer. The stability of the main recording layer increases because of the coupling with the stabilization layer 120 and because of the decrease of the demagnetization field that the main recording layer experiences. This increase in stability of the main recording layer can be traded off against the decreasing average magnetic grain volume in the main recording layer. However, in this AFC structure the net MrT of this media is reduced (net MrT=(MrT)ML−(MrT)SL) causing an increase in the effective electronic noise and a reduction in total signal-to-noise ratio (SNR) (total SNR=Media SNR+Electronic SNR).
The magnetic media structure of FIG. 1 lacks optimal magnetic properties because of high noise resulting from high magnetic exchange coupling between grains. Therefore what is needed is a magnetic media structure that is useable for high-density recording, has a high MrT and is stable.